Practice for Test 2, No. 1

1. A rectangular loop of wire has an area A. It is placed perpendicular to a uniform magnetic field B and then spun about an axis along it's diameter at a frequency f. The maximum induced emf is a) BAf. (b) BAf. (c) 2BAf. (d) 2 pi  BAf. (e) 4 pi BAf.

2. A current is in a long straight wire. The direction of the current is out of the page, and is decreasing. A loop of wire in the plane of the page is placed to the right of the long wire. Which of the following statements is true? (a) There is no induced current in the loop. (b) There is an induced current in the loop, and it flows counterclockwise. (c) The is an induced current in the loop, and it flows clockwise. (d) The is an induced current in the loop, but there is not enough information to determine its direction. (e) There is an induced current in the loop, and it flows from the north pole to the south pole.

3. "The induced current in a coil will be created in such a way that the current will oppose the change that made it." This is best described as a statement of (a) Maxwell's Law. (b) Faraday's Law. (c) Ohm's Law. (d) Burke's Law.(e) Lenz' Law.

4. If an electron vibrates up and down 1000 times each second, it generates an electromagnetic wave having a (a) period of 1000 s. (b) speed of 1000 m/sec. (c) wavelength of 1000 m. (d) frequency of 1000 Hz. (e) wavelength of 1000 cm.

5. Consider the following electromagnetic waves: x-ray with a frequency of 10E15 Hz Visible light with a frequency of 10 Hz Radio wave with a frequency of 10E-2 Hz. Which wave has the longest wavelength? (a) The x-ray. (b) The visible light. (c) The radio wave. (d) Since they are all electromagnetic waves, their wavelengths must all be the same. (e) All of the above (unless it is Wednesday, when the answer is none of the above).

6. According to Faraday's Law, the induced voltage in a coil is given by ( is the magnetic flux) (a) - (numer of turns) times (the change in flux per unit time). (b) (number of turns) times (the change in flux per unit time). (c) k q1 q2/r^2. (D) - k q1q2/r^2. (e) Ed.

7. The source of all electromagnetic waves is (a) heat. (b) magnetic fields. (c) electric fields. (d) vibrating charges. (e) None of the above.

8. A beam of light emerges from water into air at an angle. The beam is bent (a) towards the normal. (b) 48 degrees upward. (c) away from the normal. (d) 96 degrees upward. (e) not at all.

9. An object is in front of a convex mirror, a distance greater than the focal length from the mirror. The image is: (a) real, inverted, and smaller (b) virtual, inverted, and larger (c) real, inverted, and larger (d) virtual, erect, and smaller (e) real, erect, and larger

10. Somewone asks you: Will a diverging mirror always produce a virtual image? You reply: (a) Yes. (b) No. (c) Who cares? (d) Beats the heck out of me. (e) Get me outta here. (Hint: the answer is not (c), (d), or (e)).

11. The focal length of a plane mirror is (a) not defined. (b) zero. (c) 5 feet. (d) 20 feet. (e) infinite.

12. In a double slit experiment, the slit separation is doubled. This results in: (a) an increase in fringe intensity (b) a decrease in fringe intensity (c) a halving of the wavelength (d) a halving of the fringe spacing (e) a doubling of the fringe spacing

13. In a single slit, if you wanted to increase the separation between minima, you should (a) increase the slit width. (b) decrease the slit width. (c) increase the brightness of the light. (d) decrease the brightness of the light. (e) None of the above.

14. Which of the following possibilities will produce a higher resoltion? (a) Increasing the distance from your eye to the lens. (b) Decreasing the size of the lens or apperature. (c) Increasing the wavelength of light being used to view the object. (d) Decreasing the wavelength of light being used to view the object. (e) All of the above.

15. An object is examined using a simple magnifier. If the lower half of the magnifying lens is covered, what will happen to the image? (a) The lower half of the image will disappear. (b) The upper half of the image will disappear. (c) The magnification will be cut in half. (d) Nothing will change, except that the image will not be a bright. (e) Since the image is contained in the lens, when you cover up half of the lens there will not be enough room for the image anymore. The image will come squirting out of the lens, probably shooting your eye out.

16. The voltage across the input terminals of a transformer is 110 V. The primary has 25 loops and the secondary has 50 loops. The voltage the transformer puts out is (a) 25 V. (b) 55 V. (c) 110 V. (d) 220 V. (e) None of the above.

17. An FM station uses waves of frequency 10^8 Hz. What is the wavelength in meters of that electromagnetic wave? (a) 30. (b) 300. (c) 3. (d) 1/3. (e) 1/30.

18. A 2 m tall person viewing his full length image in a plane mirror requires a mirror that is at least (a) .5 m. (b) 1 m. (c) 2 m. (d) 3 m. (e) It depends on how far from the mirror the person is standing.

19. The first order maximum for a particluar diffraction grating occurs at an angle of 2o (two degrees). The second order maximum will occur at an angle of (a) 0o. (b) 1o. (c) 2o. (d) 3o. (e) 4o.

20. A laser beam is produced within a material of index of refraction n. The critical angle for total internal reflection is measured to be 30 degrees. What is the index of refraction of the material if the material is placed in air, which has an index of refraction equal to 1? (a) 0. (b) 0.866. (c) 0.500. (d) 1.154. (e) 2.000.

21. A rectangular loop of width d is placed in a magnetic field pointed into the page. The magnetic field is such that part of the loop is in the magnetic field, and the rest is outside of the field.. The loop moved toward out of the field at a constant velocity v. (a) Will a current be induced in the loop? If so, in what direction will the current be produced? EXPLAIN YOUR ANSWER CLEARLY AND PRECISELY. (b) Starting with Faraday's Law, DERIVE an expression for the induced emf in the loop.

22. An electromagnetic wave is created as a result of a charge vibrating at a frequency at 10 Hz. The distance between the extreme ends of the vibration is .01 m. Determine the period, angular frequency, amplitude, and wavelength of the resulting electromagnetic wave.

Answer key: 1.D 2.A 3.E 4.D 5.C 6.A 7.D 8.C 9.D 10.A 11.E 12.D 13.B 14.D 15.D 16.D 17.C 18.B 19.E 20.E

Practice for Test 2, No. 2

1. A certain transformer doubles its input voltage. If the primary coil has 10 Amps of current, then the current in the secondary coil is (a) 5 Amps. (b) 10 Amps. (c) 20 Amps. (d) 40 Amps. (e) None of the above.

2. A square loop (side L) of wire moves with a velocity v toward the right of the page. It passes through a constant magnetic field, directed into the page. The emf generated is (a) BLv. (b) qvB. (c) B^2 L^2 v^2 . (d) ILB. (e) Since B = const, and Area = const, the emf=0.

3. Which of the following waves travel at the highest velocity? (a) X-rays. (b) Ultraviolet waves. (c) Visible light. (d) Radio waves. (e) They all travel at the same velocity.

4. A device that transforms electrical energy to mechanical energy is a (a) generator. (b) motor. (c) transformer. (d) magnet. (e) None of these.

5. If an electron vibrates up and down 1000 times each second, it generates an electromagnetic wave having a (a) period of 1000 s. (b) speed of 1000 m/sec. (c) wavelength of 1000 m. (d) frequency of 1000 Hz. (e) wavelength of 1000 cm.

6. Which of the following is fundamentally different from the others? (a) Sound waves. (b) X-rays. (c) Gamma rays. (d) Light waves. (e) Radio waves.

7. Someone asks you: Will a converging mirror will always produce a real image? You reply: (a) Yes. (b) No. (c) Who cares? (d) Beats the heck out of me. (e) Get me outta here. (HINT: THE ANSWER IS NOT (c), (d), OR (e)).

8. For an incident ray of light, the angle of incidence equals the angle of reflection (a) always. (b) only when the surface is perfectly smooth. (c) only if the reflecting surface is glass. (d) only if the reflecting surface is perfeclty flat (ie, not curved). (e) The angle of incidence never equals the angle of reflection.

9. If a light ray crosses a boundary from medium 1 to medium 2 and is refracted aways from the normal to the interface. It can be concluded that the (a) velocity of light in medium 2 is less than in medium 1. (b) velocity of light in medium 2 is greater than in medium 1. (c) light wave is spherical. (d) index of refraction of medium 2 is less than unity. (e) index of refrection of medium 1 is less than unity.

10. A converging lens will produce an erect image if (a) do = 0. (b) do < f. (c) do > f. (d) do = 2f. (e) None of the above.

11. In an talk given to the Affiliate Society Council of Dayton in February 1992, Dr. John Mayo, President of AT&T Bell Laboratories stated that with optical fiber technology, it is possible to transmit the information in every book that has ever been written from one location to another in about 20 minutes. Optical fiber technology is largely based upon the process of (a) constructive interference. (b) destructive interference. (c) diffraction. (d) reaction. (e) total internal reflection.

12. A double slit interference experiment is set up in a chamber that can be completely evacuated. With monochromatic light, an interference pattern is observed when the container is open to air. If the wavelength of the incident light is slowly increased, a careful observer will note that the interference fringes (a) disappear completely. (b) move further appart. (c) move closer together. (d) do not change at all. (e) change color more toward the red.

13. For a single slit diffration pattern, the angular location of maxima are given by (a) sin theta = n lambda/2d; n an integer (including zero). (b) sin theta = n lambda/d; n an integer, including zero). (c) sin theta = n lambda d; n an integer (including zero). (d) sin theta = m lambda/2d; m = 3,5,7,... and zero (e) sin theta = m lambda d/2; m = 3,5,7,... and zero

14. Which of the following possibilities will produce a higher resoltion? (a) Increasing the distance from your eye to the lens. (b) Decreasing the size of the lens or apperature. (c) Increasing the wavelength of light being used to view the object. (d) Decreasing the wavelength of light being used to view the object. (e) All of the above.

15. An object is examined using a simple magnifier. If the lower half of the magnifying lens is covered, what will happen to the image? (a) The lower half of the image will disappear. (b) The upper half of the image will disappear. (c) The magnification will be cut in half. (d) Nothing will change, except that the image will not be as bright. (e) Since the image is contained in the lens, when you cover up half of the lens there will not be enough room for the image anymore. The image will come squirting out of the lens, probably shooting your eye out.

16. A 10 turn conducting loop with an area of 3.0 m2 spins with an angular frequency of 10 rad/sec in a magnetic field of 0.50 T. The maximum emf that can be generated is (a) 300 V. (b) 150/2 V. (c) 150.0 V. (d) 600 V. (e) 6000 V.

17. The frequency of an electromagnetic wave that has a wavelength of 300,000,000 m is (a) 100 Hz. (b) 10 Hz. (c) 1 Hz. (d) 0.1 Hz. (e) 0.01 Hz

18. For a single slit (slit width D = .001 cm, wavelength = 7 x 10E-5 cm), the angular location of the second order minimum is given by (a) sin theta = .07. (b) sin theta = .14 (c) sin theta = .7. (d) sin theta = 1.4. (e) None of the above.

19. A 3 cm high object is in front of a thin lens. The object distance is 4 cm and the image distance is -8 cm. The image height is: (a) 0.5 cm . (b) 1 cm . (c) 1.5 cm . (d) 6 cm . (e) 24 cm.

20. A soap bubble appears green ( = 540 nm) at its point nearest the viewer. What is its minimum thickness? Assume n = 1.35. (a) 10 nm. (b) 100 nm. (c) 500 nm. (d) 1000 nm. (e) 1 x 1056 nm.

21. A virtual image of a distant object is formed 40 cm from a mirror. If the object is moved in to a point 20 cm from the mirror, find the location of the new image. Is the new image virtual or real? Draw a clear ray diagram in support of your calculations.

22. A material (index of refraction = 1.20) is floating on a layer of water (index of refraction 1.33). What is the minimum required thickness of this material to produce destructive interference in the reflected light (use light of wavelength 500 nm)?

Answer key: 1.A 2.A 3.E 4.B 5.D 6.A 7.B 8.A 9.B 10.B 11.E 12.B 13.D 14.D 15.D 16.C 17.C 18.B 19.D 20.B